Study on the gas-sensitive properties for formaldehyde based on SnO2-ZnO heterostructure in UV excitation

The polyporous SnO2-ZnO composites were synthesized by a water-bath method. The 3D center-hollow architecture and polyporous surface were also confirmed by field-emission scanning electron microscope (FE-SEM) and the Brunauer-Emmett-Teller (BET) specific surface area. Meanwhile, structural properties of SnO2-ZnO have been investigated by trans-mission electron microscopy (TEM) in 1 mol% SnO2-ZnO. The results of photoelectric gas-sensing demonstrated that the 1 mol% SnO2-ZnO gas-sensor exhibits not only an excellent response to formaldehyde (HCHO) but also superior sensitivity to low HCHO concentration. The response of 1 mol% SnO2-ZnO for the 1 ppm HCHO has reached 30% at room temperature (25 °C), and a detection limit of 0.1 ppm HCHO was achieved. The behavior of photogenerated charge is discussed in detail by means of the surface photovotage (SPV) and the transient photovoltage (TPV) techniques. It was found that the as-prepared 1 mol% SnO2-ZnO composites showed excellent separation and transfer efficiency of photogenerated charges carriers. What's more, the TPV spectrum analysis provides convincing evidence that the addition of excess SnO2 is unfavorable to the transfer of electrons so as to reduce the sensitivity of SnO2-ZnO for target gas. This result offers a new window to explain the effect of SnO2 concentration on the gas sensing characteristics, and provide more information on the fabricating composite materials for gas sensors.